Apparatus for measuring the speed of flowing media

ABSTRACT

Apparatus for measuring the speed of media flowing in conduits is specifically concerned with the measuring of the speed of blood flowing in its channels. The apparatus is using ultrasound according to the Doppler principle method and is particularly characterized in that it has a double measuring system each containing a separate sender-receiver and that the two measuring systems are combined in such manner that the senders-receivers contained therein have sending-receiving directions which form an angle of 90*.

United States Patent Fahrbach Oct. 16, 1973 [54] APPARATUS F ORMEASURING THE SPEED 3,097,526 7/1963 Fischbacher 340/5 S 3,554,030l/l97l Peronneau 340/3 D OF FLOWING MEDIA Kurt Erich Fahrhach,Wiesbaden-Schierstein, Germany [75] Inventor:

Assignee: Siemens Aktie ngesemschaft,

Erlangen, Germany [22] Filed: Jan. 10, 1972 [211 App]. No.: 216,832

Related US. Application Data Continuation of Ser. No. 849,812, Aug. 13,1969, abandoned.

[52] US. Cl. 340/3 D, 73/194 A [51] Int. Cl G015 9/66, GOlp 5/00 [58]Field of Search 340/3 D, 5 S;

References Cited UNITED STATES PATENTS 6/1932 Chilowsky 340/3 D PrimaryExaminerRichard A. Farley Attorney-Richards & Geier [5 7] ABSTRACT 2Claims, 3 Drawing Figures f0\ fd1 f 9 5d. 1 1? 6 y fi'fdj 7f 73 72 1 A6]L i Z I 75 4 4 2 4? APPARATUS FOR MEASURING THE SPEED OF FLOWING MEDIAThis is a continuation of application Ser. No. 849,812 filed Aug. 13,1969 and now abandoned.

This invention relates to an apparatus for measuring the speed of mediaflowing in conduits, more particularly the speed of blood flowing in itschannels, by the use of ultrasound according to the Doppler principlemethod. The invention is particularly concerned with a measuringinstrument containing an ultrasound sending and receiving system whichconsists of an ultrasound sender and receiver. The terms sender andreceiver as used herein are meant to describe an electro-acousticconverter consisting of barium titanate or the like.

The magazine Ultrasonics in its January 1966 issue, page 22, described aknown measuring device of this type wherein the instrument is directedat an angle 4) to the blood vessel being examined. The frequencyshifting Af taking place on the ground of the Doppler principle betweenthe emitted ultrasound frequency f, and the received frequency freflected by the flowing blood corpuscles, amounts in the firstapproximation to A f (2vf /c) cos d: whereby f,, is the senderfrequency, v is the speed of the flowing blood, c is the speed of soundspreading and is the angle of incidence of ultrasound. A f is themeasurable quantity for the speed which is to be determined, since allother quantities are known. It appears from the above equation for A fthat if the incidence of the sender energy is a perpendicular one(namely, when d: 90 and cos no measurement is possible and that in orderto obtain a precise speed measurement it is essential to have a precisedetermination and a precise maintenance of the angle. However, in actualpractice it is hardly possible to comply with this requirement and thenonly with great difficulties and great expenditure. Thus, for example,blood vessels in a human body change their location in the surroundingtissues under the action of blood pulsations (in a manner similar tothat of a freely lying garden hose when water is turned on). Thus theknown instrument could be used to produce quantitatively usable resultsonly if measurements took place in connection with previously freed andfixed conduits. On the other hand, the measuring of the speed of bloodflow should be carried out quickly, simply and without endangering thepatient by average workers having no special knowledge.

An object of the present invention is the provision of means for solvingthis problem.

Other objects of the present invention will become apparent in thecourse of the following specification.

The present invention accomplishes this objective despite the fact thatthe equation A f (2vfi,/c) cos 4) apparently does not provide anypossibility for a precise determination of the speed V unless the angle4) is also precisely determined and maintained, which, as stated above,is not easily possible.

According to the present invention a double measuring device is providedand the two measuring devices are so combined that the sending-receivingdirections of the senders-receivers contained therein form an angle of90.

The present invention is based on the following considerations:

One sender emits with the frequency f and its related receiver receiveswith the frequency f The difference in frequency A j =f f, correspondsto the above indicated formula for A f. The other receiver receivesultrasound energy emitted by the other sender after its refection by theflowing blood corpuscles with the frequencyf The frequency break A f,between the sending frequency f of the second sender (which should havethe same sending frequency as the first sender) and f then amounts to(2vfi,/c)cos(90-). due to the shifting to the extent of of thearrangement of the measurers. If measurements are taken simultaneouslyor practically simultaneously with both measurers, then v (up to thedirection) is always the same and the expression 2vf /c is a constantone, merely equal to k. Then A f kxcos d) and A f =kxcos(90-) (there isminus k here'since the speed v for the second mea-' surer has a reversedirection from that of the first measurer).

The two results A f, and A f can be calculated as follows:

Whereby v which is the sole unknown quantity can be calculated fromabove independently of the angle (1).

Thus the present invention makes it possible by using the Dopplerprinciple to determine the speed independently from the angle. Thus theapplication of the instrument has no critical significance at all. Themovement of the vessel during the measurement which causes a change inthe direction of sound toward the vessel also has no influence upon themeasuring.

The present invention is usable specifically for measuring the flow ofblood. However, it is also usable in the same manner for technicalpurposes, such as the measuring of speed of media flowing in flexiblehose.

According to a further feature of the invention the values obtained fromultrasound receivers are treated electronically, namely theabove-mentioned calculations are carried out by a calculator, so thatthe desired result is immediately available and specifically measuredvariations in speed can be quickly determined.

It is within the scope of the present invention to replace a separatesender and receiver in each device by a single electro-acousticconverter operating alternately as a sender and as a receiver. If eachdevice contains a separate sender and receiver, they are placed one nextto the other with about the same sending or receiving direction.

The invention will appear more clearly from the following detaileddescription when taken in connection with the accompanying drawing,showing, by way of example only, a preferred embodiment of the inventiveidea. 1

In the drawing:

FIG. 1 illustrates diagrammatically, partly in section, the apparatus ofthe present invention in use;

FIG. 2 is a switch diagram of a device electrically calculating themeasurements obtained by an apparatus of the present invention;

FIG. 3 shows an instrument of the present invention, partly in side viewand partly in section.

FIG. 1 shows the outer surface 1 of the body of a patient, a bloodvessel 2, the instrument 3 and two electro-acoustical piezo-electricalconverters 4 and 5, each of which operates alternately as ultrasoundsender and ultrasound receiver. The flow of blood in the blood vessel 2is indicated by the arrow 2'. The senders-receivers 4 and are soarranged in the instrument that their sending-receiving directionsindicated by the double arrows 4 and 5' form an angle of 90.Furthermore, the senders-receivers are so arranged in the instrumentthat the directions 4', 5' intersect each other at a desired distance abelow the lower edge 1' of the instrument. The drawing shows that thevessel to be examined is located at this distance below the body surface1 and that the lower edge of the instrument is placed upon the surface 1of the body. The angle between the direction of the rays of theultrasound unit 4 and the flow direction 2' of the blood has beenindicated at (b. Therefore, the direction of rays of the sender-receiver5 with the blood flow has the angle 90 As shown in FIG. 2, thesender-receiver 4 is connected to the device 6 and the sender-receiver 5is connected to the device 7. Each of the devices 6 and 7 contains ahigh frequency generator for exciting the corresponding sender with thesender frequency and a demodulator which transforms signals supplied bythe corresponding receiver, which have a frequency shift relatively tothe sender signals depending upon blood flow speed, into analogoussignals (A f1, fz) suitable for treatment in the calculator 8. Each ofthese analogous signals is transmitted through a conduit 9 or 10 to asquaring member 11 or 12 in the calculator 8 and it is squared therein(into A f ;A ff). The outgoing signals of the squaring members 1 1 and12 are transmitted through conduits 13 and 14 to an adding member 15 inwhich they are added /A f A f The outlet of the adding member 15 isconnected to the root extracting member 16 in which a s uare root of thesummed signal is produced f, A f The divider l6 divides the result bythe constant f /c. This step also carries out the calibration of theapparatus. The outlet of the member 16' also constitutes the outlet ofthe calculator and is connected to an indicating device 17 whichindicates the speed of the blood flow and, if desired, inscribes theindicated values.

The boxes of FIG. 2 indicating the individual electronic steps containinscriptions showing the formulae involved in the calculations.

FIG. 3 shows in greater detail the instrument shown onlydiagrammatically in FIG. 1. As also indicated in FIG. 1, the twosenders-receivers 4 and 5 are so mounted in the cylindrical body 3 thatthe directions of their rays form a right angle with each other. The rayemitting surfaces of the two ultrasound sendersemitters 4 and 5 arelocated in a space 19 closed by a diaphragm 18 and filled with a liquid,such as water, so that the emitted ultrasound and the receivedultrasound both pass through the liquid in the space 19. When theinstrument is placed upon the surface of a body, the diaphragm l9 adaptsitself to the body surface, so that the ultrasound senders-receivers 4and 5 will be coupled by the liquid to the body of the person beingexamined. The ultrasound senders-receivers 4 and 5 are connected by acable 20 with the devices 6 and 7 (FIG. 2). A suction cup 21 connectedwith the casing 3 is used to attach the instrument to the body surfaceof a patient. Furthermore, the casing 3 can be provided with adiametrically extending slit 22 containing a belt which can be used forattaching the instrument to the body of the patient. Finally, it also ispossible to use glue for attaching the instrument to the body surfacewhich is being examined.

If the two senders are operated with the same frequency, it is advisableto use the so-called countercontact impulse drive wherein thesenders-receivers 4 and 5 operate alternately, in order that nodisturbing echoes should extend from one sender-receiver system into theother one.

Another type of decoupling which can be used for continuous linemeasurements, consists in that the individual systems operate withdifferent frequencies (for example, 5 MHz and 7 MHz). However, thisarrangement makes it necessary prior to the calculated amalgamation ofthe two frequency shiftings A f, and A f to lower that value which wasproduced by the system having a higher sender frequency, for example, byvoltage division in relation to the sending frequency. The switchdiagram of FIG. 2 indicates this by showing by broken lines a divisiondevice 10 which, of course, could be combined with the device 10.

According to a further feature of the present invention, it is possibleto use only one electro-acoustical converter (4, 5) for eachsender-receiver system and yet to provide continuous line operations. Inthat case, however, a high output of the sender frequency f, will lie atthe inlet of the receiving amplifier, as well as a very small output ofthe receiver frequency f The two frequencies lie comparatively close toeach other, so that a beat is produced whereby the sender frequency actsas the carrier frequency which is modulated with A f--f,,+ f,,. Thisfrequency mixture is rectified by a switched in diode, whereby thepre-voltage will correspond to about the amplitude of the senderfrequency and thereafter only the modulated voltage will remain which asan analogous value can be used as a basis for the further calculatingprocess.

A further embodiment of the present invention consists in that a singleinstrument containing two senderreceiver systems can be used formeasuring different depths a if at least one of the two systems ismounted movably in the direction of the straight line connecting the twosystems, while the angle position of the two systems remains unchanged.Many solutions are available for carrying out this movement and they areall included in the framework of the present invention. Specifically thedevices can move upon slides or in dovetailed guides. The shifting canbe advantageously carried out by a rotary pin which can be combined witha gauge indicating directly the set value of a.

I claim:

1. An apparatus for measuring the speed of flowing media, particularlythat of blood, by the use of ultrasound according to the Dopplerprinciple method, said apparatus comprising a double ultrasoundmeasuring system, each of said systems having a sender-receiver, thesending-receiving directions of said systems converging at an angle of90 to each other, and an electronic calculator connected with saidsystems for calculating the measured difference frequency between theemitted and received frequency of each of said systems, said calculatorcomprising two squaring members for simultaneously and separatelysquaring the electric voltages corresponding to difference frequencies,an adding member for adding the squared voltages, a root extractingdevice for calculating the square root of the added voltages, and anadjustable dividing member, said members being interconnected in thestated order,

said dividing member comprising an outlet for an indishifting means forshifting at least one of said systems cator. relatively to the othersystem in the direction of a 2. Apparatus in accordance with claim 1,wherein straight line connecting the two systems. said double ultrasoundmeasuring system comprises

1. An apparatus for measuring the speed of flowing media, particularlythat of blood, by the use of ultrasound according to the Dopplerprinciple method, said apparatus comprising a double ultrasoundmeasuring system, each of said systems having a sender-receiver, thesending-receiving directions of said systems converging at an angle of90* to each other, and an electronic calculator connected with saidsystems for calculating the measured difference frequency between theemitted and received frequency of each of said systems, said calculatorcomprising two squaring members for simultaneously and separatelysquaring the electric voltages corresponding to difference frequencies,an adding member for adding the squared voltages, a root extractingdevice for calculating the square root of the added voltages, and anadjustable dividing member, said members being interconnected in thestated order, said dividing member comprising an outlet for anindicator.
 2. Apparatus in accordance with claim 1, wherein said doubleultrasound measuring system comprises shifting means for shifting atleast one of said systems relatively to the other system in thedirection of a straight line connectiNg the two systems.